Fiber reinforced pipe

ABSTRACT

A flexible, fiber reinforced pipe has been invented for conveying fluids. The pipe is flexible enough to be spoolable, even under winter temperature conditions. The pipe can contain pressure, when buried, unrestrained and bent. The pipe exhibits impact resistance under normal handling and can be formed using a continuous process, such that it can be manufactured as it is being laid. A flexible, fiber reinforced pipe includes an inner tubular liner having an inner surface and an outer surface; a first layer of reinforcing fibers helically wrapped about the inner liner and in direct contact therewith; an outer layer of reinforcing fibers helically wrapped about an underlying layer of reinforcing fibers and in direct contact therewith; and an outer tubular sheath applied over the outer layer in direct contact therewith.

BACKGROUND OF THE INVENTION

Flexible pipes are needed for conveying fluids under pressure such assour gas, carbon dioxide and hydrocarbons.

It is desirable that the pipe be spoolable without collapsing orbuckling, even in low temperature environments. The pipe must also becapable of containing high pressure flows under conditions of use, suchas when buried, unrestrained and bent.

SUMMARY OF THE INVENTION

A flexible, fiber reinforced pipe has been invented for conveyingfluids. The pipe is flexible enough to be spoolable, even under wintertemperature conditions. The pipe can contain pressure, when buried,unrestrained and bent. The pipe exhibits impact resistance under normalhandling and can be formed using a continuous process, such that it canbe manufactured as it is being laid.

In accordance with one aspect of the present invention, there isprovided a flexible, fiber reinforced pipe comprising: an inner tubularliner having an inner surface and an outer surface; a first layer ofreinforcing fibers helically wrapped about the inner liner and in directcontact therewith; an outer layer of reinforcing fibers helicallywrapped about an underlying layer of reinforcing fibers and in directcontact therewith; and an outer tubular sheath applied over the outerlayer in direct contact therewith.

The underlying layer of reinforcing fibers can be the first layer ofreinforcing fibers or intermediate layers of reinforcing fibers appliedbetween the first layer and the outer layer. Where the pipe includesonly two layers of reinforcing fibers, the first layer and the outerlayer, the outer layer is wrapped in a helical direction opposite(clockwise or counterclockwise) to the first.

Where the pipe includes one or more intermediate layers of reinforcingfibers in addition to the first layer and an outer layer, there must beat least one layer of reinforcing fibers wrapped in a positive helicaldirection and at least one layer of reinforcing fibers wrapped in annegative helical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partly broken away in successive layers, of anembodiment of a pipe in accordance with the present invention.

FIG. 2.is a sectional view taken along lines II-I of FIG. 1.

FIG. 3 is a side view, partly broken away in successive layers, ofanother embodiment of a pipe in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a pipe according to the present invention is shown.The pipe includes an inner tubular liner 10 having an inner surface 12and an outer surface 14, a first layer 16 of reinforcing fibershelically wrapped about the inner liner and in direct contact with theouter surface thereof, a second layer 18 of reinforcing fibers helicallywrapped about the first layer of reinforcing fibers in direct contacttherewith and an outer sheath 20 applied over the second layer and indirect contact with the second layer of reinforcing fibers. The firstlayer of reinforcing fibers are wrapped either clockwise orcounterclockwise and the second layer is wrapped in the other of theclockwise or counterclockwise direction, when compared to the firstlayer. Thus, it is said that one layer is wrapped at a positive helicalangle and the other layer is wrapped in a negative helical angle.

Inner tubular liner 10 provides little or no structural support for thepipe. Preferably, the liner is selected to support the loads induced byapplication of the outer layers about it such as during the windingprocess and the subsequent extrusion of outer sheath 20. Further, theliner is selected to act as a leak and permeation bladder. The linershould be formed of the most molecularly impervious polymer that meetsacceptable material costs, as determined by a cost benefit analysis.Generally, the liner should be selected such that the only leakage isdiffusion of gaseous components of the fluid being conveyed. Obviously,the elimination of gaseous diffusion through the liner is preferred. Aswill be appreciated, the liner is selected to be substantially resistantto degradation by the fluid to be passed therethrough.

The liner is formed of a polymer having bending strains of about 2 to 5percent such as a thermoplastic or an elastomer. Thermoplastics caninclude, for example, nylons, cross-linked polyethylene (PEX),polytetrafluroethylene (PTFE), higher temperature engineered polymers orhigh density polyethylene (HDPE). Elastomers can include, for example,rubbers and nitrites. For petroleum operations, HDPE is particularlyuseful as it provides good chemical compatibility with many oilfieldchemicals at a low cost.

In some embodiments, the liner is filled, for example, with amorphousclays, chopped glass or carbon fibers. These materials can enhance linerstability, for example, against low temperature cracking, againstpolymer creep for long term integrity and may enhance the initialstrength of the liner following extrusion. The fibers can be aligned orrandom.

Outer sheath 20 surrounds fiber reinforcements 16, 18. While the pipewill function to contain pressurized fluids without the outer sheath, itis useful as it acts to protect the fiber reinforcements from damage, asby abrasion, and assists in stabilizing and holding the fibers in place.The outer sheath can be formed of any flexible material that can protectthe fiber reinforcements to some degree. The outer sheath can be, forexample, a polymer such as a thermoplastic or a thermoelastomer and canbe fiber-filled, if desired. Some useful polymers are, for example,polyethylene or nylon, which are useful for their abrasion resistance aswell as their low cost. As will be appreciated with consideration as tothe intended use of the pipe, outer sheath 20 can be selected to besubstantially resistant to degradation by environmental effects (i.e.ultraviolet light, weather, etc.) and by the chemicals that may come incontact with it.

As desired, the outer sheath can include or have attached theretoidentifiers such as, for example, paint, coloration, bar-coding, chips,etc. or materials facilitating use or installation such as, for example,electrically conductive wire or survey locatable metal parts. Where suchmaterials are used however, which can abrade fiber reinforcements, suchmaterials should be spaced or shielded from contact with the fiberreinforcements, as by imbedding or encapsulating within the outersheath.

In a two layer pipe such as is shown in FIG. 1, layers 16, 18 of fiberreinforcements are configured with one layer wound in a positive orclock-wise helical direction and the other layer wound in a negative orcounter-clockwise helical direction. A layer is one or moresubstantially continuous reinforcement fiber wound onto the liner or theunderlying fiber layer at the same angle and direction. As will beappreciated substantially continuous reinforcements are those of longlength, extending along the length of the reinforcement bundle, ratherthan being formed of chopped or discrete fibers that are matted, wovenor otherwise treated to hold them together.

The layers 16, 18 can each be configured in various ways from pipe topipe and from layer to layer. For example, the layers of fiberreinforcements in any one pipe can vary by the number and arrangement offibers in a reinforcement bundle (also termed a tow), type of fiber,winding tension, helical angle of winding and/or amount of fibers in anyone layer and pipe characteristics can be controlled by selection ofthese factors.

The fiber layers in the pipe act to react axial and radial loadsresulting from, for example, internal pressure and tensile loading.Primary load is in the fiber tensile direction, since generally littleside load is induced from operational conditions. Thus, preferred fibersfor use in the pipe provide low elongation to failure, for example, ofless than 2%. The fibers should also be resistant to degradation bychemicals, such as hydrocarbons and water, intended to be handled, orenvironmentally present, during use of the pipe. Suitable fibers includeglass such as E-glass, E-CR glass or S-glass, carbon, nylon, polyesteror aramid. For petroleum operations, E- and E-CR-glass is preferred dueto its low cost and ability to carry the required loads. Elongation tofailure of glass is generally less than 0.5%.

The use of metal wires which can cause failure, as by abrasion orcutting, of reinforcement fibers should be avoided or should be out ofcontact with the reinforcement layers.

The fibers in the layers are substantially free floating between liner14 and sheath 18, being unbonded, as by use of separate adhesives, orcurable, cured or uncured polymers, so that the separate fibers, bundlesand layers remain independent and can react loads in conjunction witheach other, rather than in combination as a rigid body. For example,fibers should be used that are substantially dry such that they will notchemically bond or fuse with other fibers or to the liner or sheath. Itis to be noted that the fibers can be untreated, treated or coated andyet considered dry. Each fiber bundle can include one or more individualfibers sometimes twisted together (i.e. in the form of yarn). In oneembodiment, a useful fiber bundle contains thousands of individualfibers and is encapsulated with a polymer coating, which does notpenetrate the bundle such that the inner fibers remain dry and notchemically bonded or fused together, but are held together as a bundleby the polymer coating. Of course, where fibers are wound onto the linerwhen it is in the soft or semi-uncured state or the outer sheath 20 isapplied by extrusion, as will be described below with respect to amethod for producing the pipe, the material of the liner or sheath maymold, and adhere to some degree, to the adjacent fibers. This may reducethe effective free floating characteristics of the inner and outer-mostfibers, although the materials of the liner and sheath should preferablybe selected to avoid infiltration past the fiber reinforcements whichactually come into contact with it. Release agents or other means can beused on the sheath, liner or fibers to reduce adhesion between thefibers and the sheath or liner.

The fibers should be capable of close fitting, thus the use of largerouter diameter fibers, which do not permit close fitting should beavoided. In one embodiment using E-glass fibers, a packing density of 75to 80% has been found to be desirable. Winding tension effects packingdensity. A tension force should be used that permits packing of thefiber tows in a manner useful for carrying the required load for theintended application of the pipe. If the fiber tows are not packedsufficiently tight, there will be tightly wound fibers and loosely woundfibers in the pipe. The loose fibers will react loads differently thanthe tight fibers, so that not all fibers are being employed to carryloads simultaneously. If not all fibers are loaded substantiallyuniformly, then some fibers may break sooner, as their respective loadlimits will be reached earlier than the designed optimal limit. Inembodiments using fibers with low elongation to failure, such as glass,it is to be understood that the fibers will tend not to stretch toaccommodate slack in adjacent fibers. The effects of differentialelongation to failure should also be considered when using more than onefiber type in a particular layer. On the other hand, if the fibers arewound with undesirably high tension, fibers will tend to be brokenduring processing and handling.

The use of tapes is generally not desirable, as close fitting andindependent reaction of loads are jeopardized.

The angle of winding of each layer 16, 18 is selected as a compromise onthe various loads and conditions to which the product will be exposedduring processing and during use with respect to durability and pressurecontainment, while providing desired flexibility. In the presentinvention, the prominent condition is internal pressure containment, sothe fiber reinforcement needs to be optimized in the radial tensiledirection. Other factors that should be considered include installationpull force in the field (axial tensile force) and loads from spoolingand unspooling for transport and installation in the field. Keyresponses of the pipe under load that have to be provided through thewinding angles include axial and radial growth of the pipe under thefield conditions. Winding angles of between about 8° and 86° can beused. In one embodiment, winding angles of between 40° and 70° are used,with preferred winding angles being between 50° and 60°.

Referring to FIG. 3, there is shown another embodiment of a pipeincluding an inner tubular membrane 110, a first layer 116 ofreinforcing fibers helically wound about the inner liner, anintermediate layer 117 of reinforcing fibers helically wrapped about thefirst layer of reinforcing fibers, an outer layer 118 of reinforcingfibers helically wrapped about the intermediate layer of reinforcingfibers and a coating 120 applied over outer layer 118.

In the embodiment of FIG. 3, the layers 116, 117, 118 are formed fromglass or carbon based fibers or a combination thereof and at least twoof the layers are wrapped in opposite helical directions. Adjacentlayers can be wrapped in similar directions, but at different angles.This may be useful to reduce fiber abrasion propensity.

Production

With reference to FIG. 1, a pipe in accordance with the presentinvention can be produced by winding fiber reinforcements about an innerliner 10 to form at least one fiber reinforcement layer 16 wrappedhelically in a first direction and at least one fiber reinforcementlayer 18 wrapped in an opposite direction. Then a coating 20 is appliedover the outer most fiber layer. Preferably, the pipe is produced usinga substantially continuous process, wherein long lengths, for example of0.5 km or more, are produced either just before installing the pipe orfor spooling to be used later.

The liner can be formed in any desired way, with consideration as to theabove noted description of the liner. In a preferred embodiment, theliner is produced by extrusion, providing continuous production thereof,of course limited by raw material supply, reel handling sizeconsiderations, shipping, etc.

The liner is then wound with continuous fiber reinforcements. Thereinforcements are generally wound about outer surface 14 of the lineronce it is in the solid state. However, it is possible to apply thefiber reinforcements while the liner is in a molten, semi-molten,uncured or semi-cured state. If the outer surface of the liner is notyet solidified when the fibers are wrapped about it, the first fibersapplied over the liner may sink to some degree into the surface of theliner. This can be tolerated, although it is preferred that the fibersnot stick at all to the liner and be completely free floating.

One or more reinforcements including fibers of glass, nylon, polyesterand/or aramid are wound to form a first layer 16, which is in contactwith and covers entirely the outer surface of the liner. In oneembodiment, 32 tows each of multiple fibers are wrapped to form a singlelayer. However, any number of fibers and tows can be used depending ontow fiber count, layer characteristics which are desired to be achievedand equipment capabilities.

Winding can be accomplished by use of a winder that winds one or morefibers in a helical fashion about the liner, as it is being advanced.The fibers are preferably wound at continuous tension levels using, forexample, 5 to 10 pounds of pull force for glass. Winding tension mayvary from layer to layer to accommodate differences with respect to thefiber material used in that layer. The level of tension force whenwinding higher elongation fibers is less important than when windingbrittle fibers.

In a layer winding process, a few individual terminated fibers in abundle can be ignored and the free ends will usually be brought backinto the bundle as winding continues. A broken fiber which is wound backinto the layer recovers its loading capability within a few centimeters.While it is desirable to avoid the use of spliced tows in, or the needto splice tows during production of, a length of pipe, some splices canbe accommodated without significant adverse effects on pipe performance.An entire broken tow can be spliced back into the process for continuedpipe production by introduction back into the winding process, by use ofa stitch or glue. Preferably, however, with consideration as to thelength and the wind angle of the pipe to be produced, a tow supply isselected that does to ensure that splices need not be present along thelength of the pipe.

Second layer 18 is then wound about, in contact with, the first layer16. Process considerations as set out above are also applied in theapplication of the second layer. In one embodiment, the layers areselected to have substantially equal load carrying capability. Forexample, the first and second layers can have substantially equal butopposite winding angles and fibers applied in substantially equalquantities.

Further fiber reinforcement layers can be wound about second layer 18,as desired, such as is shown in FIG. 3. In addition, other layers can beapplied such as coatings, etc. provided that they do not interferingwith the ability of the fiber reinforcements to carry load, or otherwisesignificantly adversely effect the pipe performance.

Sheath 20 is then applied over the second layer 18, as by extrusion,spraying, dipping, tape winding, shrink wrapping, braiding, etc.

The liner is generally selected to support the loads induced byapplication of the outer layers about it such as during the windingprocess and the subsequent extrusion of the outer sheath. It is usefulto control winding tension to avoid collapse of the liner during thewinding process. Sometimes, however it is useful to support the liner toa certain extent during production by, for example, the use of rollersor internal pressure. It is also useful to use rollers or other means tourge the liner into a generally circular cross-section prior to windingto control the cross-sectional shape of the finished pipe.

Performance

For many hydrocarbon handling operations, a pipe having a 3000 psi burstis considered acceptable, a liner bend strain of about 2 to 5% andpreferably a maximum of about 3%, and a minimum bend radius of at least15× times pipe outer diameter is within desired properties. Otherperformance properties may be desired for other applications.

EXAMPLE

A pipe was produced in accordance with Table I. TABLE I Production InnerLiner Liner Material HDPE Liner OD in 3.500 Liner SDR ratio (OD/t) 17.0Liner ID in 3.088 Liner wall thickness (t) in 0.206 Continuous fiberwrap in two layers Fiber Material E-glass Wrap angle inner layer deg.+55.0 Wrap angle outer layer deg. −55.0 Number of yarns per layer 32Thickness per wrap in 0.054 Cover Cover material HDPE Cover thickness in0.100 Cover/pipe OD in 3.916 Cover ID in 3.716 Cover SDR 39.2

At design stage, it was desired that the pipe be useful for 750 psioperating pressure. Experiments showed that the pipe burst at about3,000 psi.

Pipe performance is shown in Table II. TABLE II Performance Designoperating pressure psi   750 Burst pressure psi 3,000 Fiber stresssafety factor    4.7 Axial strain %    0.3% Radial strain %    0.3%

It will be apparent that many other changes may be made to theillustrative embodiments, while falling within the scope of theinvention and it is intended that all such changes be covered by theclaims appended hereto.

1-8. (canceled)
 9. A flexible, fiber reinforced pipe comprising: aninner tubular polymeric membrane, a first layer of glass reinforcingfibers helically wound about the inner tubular membrane in a firsthelical direction, a second layer of glass reinforcing fibers helicallywrapped in a second helical direction opposite to the first helicaldirection and positioned outwardly of the first layer of reinforcingfibers, the fibers of the second layer each being independently moveablewithin the second layer and an outer coating applied outwardly of thesecond layer of reinforcing fibers, the first layer of glass reinforcingfibers and the second layer of alass reinforcing fibers each beingsubstantially free floating between the inner tubular membrane and theouter coating and being separated from contact with any metalreinforcements in the pipe.
 10. (canceled)
 11. The pipe of claim 9wherein the pipe includes at least one intermediate layer of reinforcingfibers disposed between the first layer and the second layer.
 12. Thepipe of claim 9 wherein the inner tubular membrane is a thermoplastic oran elastomer.
 13. The pipe of claim 9 wherein the outer tubular sheathis a thermoplastic or an elastomer.
 14. The pipe of claim 9 wherein theglass reinforcing fibers include E-glass.
 15. The pipe of claim 9wherein the reinforcing fibers are substantially continuous along thefirst layer and the reinforcing fibers are substantially continuousalong the second layer.
 16. The pipe of claim 9 wherein the first andsecond layers include substantially equal but opposite winding anglesand fibers applied in substantially equal quantities.
 17. The pipe ofclaim 9 wherein the first layer of reinforcing fibers includessubstantially continuous and dry fibers and the second layer ofreinforcing fibers includes substantially continuous and dry fibers.18-24. (canceled)
 25. The pipe of claim 9, wherein the first layer andthe second layer provide the pipe with controlled radial growth underload and controlled axial growth under load. 26-32. (canceled)
 33. Thepipe of claim 9 wherein the glass reinforcing fibers of the second layerare each independently moveable within the second layer by winding thefibers at the same angle and direction throughout the second layer. 34.The pipe of claim 33 wherein the glass reinforcing fibers are non-wovenin the second layer.
 35. The pipe of claim 9 wherein the glassreinforcing fibers of the first layer are each independently moveablewithin the first layer.
 36. The pipe of claim 35 wherein the glassreinforcing fibers of the first layer are each independently moveablewithin the first layer by winding the fibers at the same angle anddirection throughout the first layer.
 37. The pipe of claim 36 whereinthe glass reinforcing fibers are non-woven in the first layer.
 38. Thepipe of claim 9 wherein the first layer completely covers the innertubular membrane and the second layer forms a surface over which theouter coating is applied.
 39. The pipe of claim 9 wherein the pipe isdevoid of metal reinforcements between the inner membrane and the outercoating.
 40. The pipe of claim 9 wherein the pipe is devoid of metalreinforcements.
 41. The pipe of claim 9 wherein the glass reinforcingfibers include E-CR glass.
 42. The pipe of claim 9 wherein the glassreinforcing fibers include S-glass.
 43. The pipe of claim 9 wherein theglass reinforcing fibers of the first layer are wound at a pull force of5 to 10 pounds.
 44. The pipe of claim 9 wherein the glass reinforcingfibers of the second layer are wound at a pull force of 5 to 10 pounds.45. The pipe of claim 9 wherein the first layer and/or the second layerhas a winding angle of between 40° and 70°.
 46. The pipe of claim 9wherein the first layer and/or the second layer has a winding angle ofbetween 50° and 60°.
 47. The pipe of claim 9 wherein the second layer ofglass reinforcing fibers is applied over and in direct contact with thefirst layer of glass reinforcing fibers and the outer coating is appliedover and in direct contact with the second layer of glass reinforcingfibers.
 48. The pipe of claim 47 wherein the pipe is devoid of metalreinforcements.
 49. The pipe of claim 9 wherein the second helicaldirection has a winding angle that is substantially equal but oppositeto a winding angle of the first helical direction.
 50. The pipe of claim9 wherein the pipe includes at least one additional layer of reinforcingfibers disposed between the second layer and outer coating.